An adhesive composition containing a 2-cyanoacrylic acid ester quickly establishes a strong bonding among various types of materials attributed to the unique anion polymerization characteristics exhibited by its principal component, 2-cyanoacrylic acid ester, which initiates polymerization under the presence of weak anion provided by slight moisture or the like attached to a surface of an adherend. Accordingly, it is used as the so-called instantaneous adhesive in a wide range of fields including industrial, medical, and household applications. Because the cured product of this adhesive composition is hard and brittle, it exhibits excellent adhesion strength against shear; however, it is problematic in that peel adhesion strength and impact adhesion strength are low, and particularly cold/hot cycle resistance of the adhesion strength is inferior, particularly when it is applied between different types of adherends. Furthermore, in case of bonding flexible adherends, there is a problem of impairing the flexibility of the adherend.
To overcome these problems, modification methods have been proposed heretofore, which include adding various types of plasticizers and elastomers (see, for instance, Patent Documents 1, 2 and 3). Also proposed are methods of blending therein a poorly soluble rubber or elastomer particles (e.g., Patent Documents 4). Furthermore, also disclosed is an adhesion method using two types of adhesives, i.e., 2-cyanoacrylic acid ester and a moisture-curing adhesive at ordinary temperature, in which temporary fixation is quickly achieved and sufficiently high adhesion strength is established after certain lapse of time (e.g., Patent Document 5).
On the other hand, also known in the art is a method for improving the water-resistance of the adhesive by blending a monosilane compound or a bissilane compound in the 2-cyanoacrylic acid ester (e.g., Patent Document 6).